Phonograph record scanning device



April 13, 1943. THQMPSQ'N 2,316,637

PHONQGRAPH RECORD SCANNING DEVICE Filed'Dec'. 24, 1941 {CENTRALOR {REPRODUGING I 7 30 I NEUTRALSEUTOR ANGLE 2 6 I \QDiSECTOR I5 Fi .4. 4 27 gig 72 0 :23

, INVENZOR My, L/NCOLN THOMPSON ATTORNEY Patented Apr. 13, 1943 PHONOGRAPH nEoonn SCANNlNG nE'vicE Lincoln Thompson, Cheshire, Conn., assignor to The Soundscriber Corporation,

New Haven,

Conn., a corporation of Connecticut Application December 24, 1941, Serial No. 424,334

8 Claims.

This invention relates to phonographs and more particularly to a method of and means for improving the scanning movement of a phonograph reproducing stylus and reproducing arm across a record tablet.

In phonographs for recording dictation or other sound ondisk records, it is common practice to provide a play back reproducer on a reproducing arm in such relation to the direction of rotation of the turntable that the record groove under the reproducing stylus travels in a general direction toward the vertical axis around which the reproducing arm swings, a similar relation of the reproducing arm to tablet travel being also employed in other phonographs. When the record groove is made relatively shallow in order that the grooves may be closely spaced for economy of record space, and in other cases where the depth of the record groove is small and the general direction of groove travel under the stylus is toward the vertical axis of the reproducing arm, it-

has been found that the stylus, when in the outer turns of the spiral, tends with any slight disturbance to move out of the desired groove position and accelerate across the grooves in a direction radially outward of the record disk, and when the stylus is in the inner turns of the spiral, it tends with any slight disturbance, to move from the desired groove position and accelerate across the grooves in a direction radially inward of the record disk. These dislocations of the stylus of course interrupt reproduction from the desired groove and are very troublesome.

The difliculty has been traced to the component of force exerted laterally of the groove by friction between the reproducing stylus and the record disk. Although the lateral component-of stylus friction is very small and may often be insuflicient by itself, to force the stylus out of a groove, any slight disturbing force, such as that due to accidental jarring oi the phonograph, or due to gravity when th turntable or record disk is not in a true horizontal posiion, may add to the lateral component of stylus friction and make a total lateral force sufficient to dislocate the stylus from its desired groove position, thus preventing the desired scanning of the record. These difliculties have been found to be of special importance when reproducing from record grooves produced by an embossing rather than by a cutting recording stylus, and particularly when the tablet is madeof a plastic material.

An object of the present invention is to counteract one or more of the above difliculties, and

to improve the scanning or tracking movement of a reproducing stylus and the reproducing arm across a recor tablet.

travels underthe stylus in a general direction toward the vertical axis of rotation of the reproducing arm.

Another object is to provide a friction counteracting device of the kind referred to, adapted for convenient attachment to a reproducing arm unit, without requiring any substantial change in the original construction of the unit, or the use of any tools while attaching the device to the unit.

In accordance with the present invention, the latteral component of the force of stylus friction in the groove of a record disk, when the groove travels under the stylus in a general direction toward the vertical axis of rotation of the reproducing arm, is counteracted by a compensating force applied to a part of the stylus remote from the stylus point and in a direction urging the stylus toward a position wherein the direction'of travel of the turn of the groove under the stylus is tangent to the vertical plane including the stylus point and the vertical axis of rotation of the reproducing arm. The compensating force may be applied by a spring having one end thereof adapted for attachment to a stationary part of 'the phonograph, the other end of the spring being movable and positioned to engage in contact with the reproducing arm at a portion thereof remote from the vertical axis of the arm. The movable end of the spring is preferably arranged to urge the arm from either of two side sectors toward a central or neutral sector of the reproducing angle through which the arm swings during reproduction. The spring is preferably disengaged from contact with the arm and exerts no force thereon while the arm is within the neutral sector, but comes into action to exert Another object is to provide a device of simple and compact construction, adapted efficiently to counteract the lateral component of stylus friction on a record tablet when the record groove compensating force when the backlash" is taken up in either direction.

These and other objects and features of the invention will be apparent from the following detailed description of a preferred form illustrative of the invention, in connection with the accompanying drawing and the appended claims.

In the drawing:

Figs. 1 and 2 are an elevation and a plan, respectively. of a reproducing arm unit having a friction counteracting attachment applied thereto.

Fig. 3 is a. diagrammatic plan showing the secto the L-shaped bracket 8, which in turn is fast to the top plate 9 of the phonograph chassis.

The reproducing head 2 may be raised or lowered by the handle l0, fast to the head. The

stylus 6 engages and scans the record disk tablet H having the spirally directed record groove i2, Fig. 3, the tablet being supported on the turntable I 3' which moves the tablet from right to left, as shown in Fig. l, in a general direction toward the vertical axis 5, 5 of arm 3.

Fig. 3 shows diagrammatically, the. disk Ii havingthe spiral groove l2 having a turn thereof under the stylus 6 traveling toward the axis 5 about which arm 3 swings. On account of the friction of the stylus 6 on the disk ii, there is in general a component of frictional force urging the stylus laterally out of groove l2, the value or strength of the lateral component varying with the angular position of arm 3 and becoming zero at only one position of arm 3, indicated by the device for counteracting the lateral component of stylus friction when the reproducing arm unit is of the type illustrated in Figs. 1, 2 and 5, and the groove under the stylus travels toward the vertical axis of the arm. Device consists of a slender spring wire, bent into the formshown in Fig. 4, having'a closed loop-like clasp 2| to serve as an attachment end thereof, shaped as shown in Figs. 1, 2 and 5, to conform with the contour of the upper part of the stationary support elements 1, 8 to provide a spring gripping engagement therewith to hold the attachment end 2i fast in stationary relation with the chassis 9. It will be seen that this arrangement is of a-form adapted to be conveniently and snugly nested over the-upper ends of brackets l, 8, like a hat over a head, or a thimble overs. finger, without dot-dash line 5, i4, wherein the vertical plane" including the point of stylus 6 and the vertical axis 5, 5, is tangent to the turn of groove l2 under the stylus.

When the arm 3 is on either side of the vertical plane including line 5, l4, the lateral component of stylus friction on disk ll, increases with the angle made with the plane, and is ofmaximum value at the extreme outer position 5, I5, and the extreme inner position 5, Hi. The lateral component of friction acts in a direction away from the line 5, M, as indicated by the ar-' rows at l5 and I6, respectively, when the general direction of tr vel of the record groove under the stylus is towar the axis 5, 5. The angle l5, 5,16, within which the arm 3 swings on its vertical axis 5, 5, during reproduction, will be referred to for convenience, as the reproducing angle of the arm. Arm unit i is usually designed so that the line 5, I4 is at or not far from the middle of the reproducing angle l5, 5, H5. The path of stylus 6 across the turns of the groove l2, when arm 3 swings across the record tablet II, is shown by dotted line 3!, Fig. 3.

requiring the use of special tools or complicated operations, and withoutrequiring any substantial change from the original construction of the unit i, thus making the device of particular advantage 'for attachment to phonographs which are to be conditioned for playing records offering less stylus tracking guidance than the records for which the phonographs were originally manui'actured.

From the fixed end 2| of spring 20, projects the long horizontal arm 22 in a direction similar to reproducing arm 3, the projecting end 23 being positioned adjacent to a part 24 of reproducing arm 3 remote from vertical axis 5, 5, the part 24 being a vertical pin or other suitable part of the arm 3 and having a pair of spaced apart vertical sides 25, 26, to serve as abutments. The movable end 23 of spring 20 is preferably bent into a U-shaped form having two arms 21, 28, of the U, extending in a direction similar to that of arm 3, to provide spaced apart contacts at the inner "sides of the U, adapted to provide a "backlash engagement with the two spaced abutments 25,

23 on arm3. The spacing between contacts 21, 28, is preferably made a predetermined amount greater than that between abutments 25, 26, so that the contacts are spaced equal distances from abutments 25, 26 when the stylus is on line 5, M, the predetermined amount of greater spacing being such that arm 3 maybe swung either side Any slight disturbing force, such as that due to accidental jarring of the phonograph, or. due to gravity when the turntable or record disk is not in a true horizontal position, may add to the lateral component of stylus friction, referred to above, and make a total lateral force sufficient to dislocate the stylus from its desired groove position.

It has been found possible to counteract this difliculty by applying to a part of the reproducing stylus 6 remote from the point thereof, preferably through the medium of the reproducing arm 3 and head 2 supporting the upper end of the stylus, a compensating force in a direction urging the stylus toward the line 5, M, Fig. 3. The

of line 5, it within the central or neutral sector 29, 5, 30, wherein the lateral component of stylus friction is negligibly small, without spring 20 engaging in contact with arm 3.

When the arm 3 reaches either of the side sectors I5, 5, 29, or 30, 5, l5, where the lateral component of stylus friction reaches undesirable values, as the arm swings from the central sector 23, 5, 30, of the reproducing angle or in other words, when the "backlash is taken up, one of the contacts 21, 28, selectively engages with its cooperating abutment 25, or 26, respectively, and presses against the abutment in a direction opposing the lateral component of stylus friction, the amount of pressure increasing approximately in accordance with the increase of the angle between arm 3 and the line 5, H, or the boundary line 5, 23, or 5, 30, of the central sector. The spring device 20 is thus adapted efiiciently to counteract and compensate for the lateral component of stylus friction, and to reduce the tendency of the stylus to be dislocated from its desired groove position. Since the wire 20 is disposed close to' the unit I, it conforms compactly with the available space around the is out of contact with arm 3'when the arm is in the central sector, 29, 5, 30, so that the compensating force is zero within this sector, the as-' sembly of the spring with the unit I is facilitated; the position of the spring relatively to arm 3 is 5 more readily observed at the end 23 while adjustment of the spring is being made, thus facilitating adjustment of the spring; and any tendency of the spring to introduce friction on the movement of arm 3, is completely avoided while the arm 3 isin the central sector. It will be seen also that the described arrangement of the compensating spring combination with reproducing arm 3, avoids the introduction of anyforce tending to urge the free end or arm 3 up or down, and thus avoids the production of increased friction from this cause at pivots 5, 5.

When disk records of smaller diameter than that shown in Fig. 3 are to be employed, and the spiral record groove occupies an area ex tending merely within the neutral sector 29, 5, 30 and the side sector It, 5, 29, the reproducing angle of arm 3 will be limited to angle l6, 5, 30, and only the contact 21, and the abutment will be operative to engage in contact, while contact 28 and abutment 26 would be inoperative and could obviously be omitted.

Various changes may obviously be 'made in the compensating device 20, a preferred form of which has been described by way of illustration, 30 and in the exact shape of the attachment end of device 20, as well as in the shape and location of the arm 22 and the movable end 23, without departing from the present invention as' defined in the appended claims.

I claim:

1. In combination'with a phonograph unit of the type including a reproducing arm, means vfor supporting said arm including bearings having a vertical axis of rotation for the arm and a stylus 40 actuated reproducing device on said arm remote from said vertical axis, said combination including an abutment on said arm remote from said vertical axis, a slenderspring having one end thereof in fixed relation with said arm, supporting means, the, other end of said spring bein movable and positioned adjacent to but spaced from said abutment while the arm is swung witha in a predetermined neutral sector or the reproducing angle, said neutral sector including an arm position wherein the lateral component of stylus friction in a record groove is zero, the

movable end of said springengaging in contact with said abutment while the arm is within a sector of thereproducing angle outside of and on apredetermined side or said neutral sector.

2. In combination with a phonograph-unit or the type including a reproducing arm, means for supporting said arm including bearings having a vertical axis of rotation for the arm, and a stylus actuated reproducing device on said arm remote from said vertical axis, said combination including two spaced apart abutments on said arm remote from said vertical axis, a slender spring having one end thereof in fixed relation with said arm supporting means, the other end of said spring being movable and havingtwo spaced apart contacts positioned adjacent to but spaced from said abutments while the arm is vswunE within a predetermined neutral sector or the reproducing'angle, one of said contacts being positioned to engage one of said abutments when the arm is swung into a sector or the reproducing angle at one side of said neutral sector, the other of said contacts being positioned to engage the 15 other of said abutments when the arm is swung into a sector of the reproducing angle at the other side of said neutral sector.

3. A device for counteracting the lateral component of the force of phonograph stylus friction on a record disk, when the stylus is carried by a reproducing arm having a vertical axis of rotation remote from the stylus, and when the general direction of travel of the record groove under the stylus is toward said vertical axis, said device including a slender wire spring having an attachment end to be made last to a relatively stationary part of the phonograph, and a movable end bent into, the shape of a U forengaging said reproducing-arm at spaced apart portions thereof remote 'from said vertical axis, the arms of the U being spaced apart a predetermined distance greater than that between the portions of the arm to be engaged thereby.

4. In a phonograph including a reproducing arm, a stylus carried by said arm, means for supporting said arm with a vertical axis of rotation remote from said stylus, means for causing the groove of a record disk to travel under said stylus, and means for applying a force to a part of said arm remote from the pointthereof, said means applying said force in a direction urging the stylus toward a position wherein the direction of travel of the groove under the stylus is tangent to the plane including the stylus point and said vertical axis, said means being inactive I when said stylus lies within a predetermined neutral reproducing sector.

v 5. In a phonograph including a reproducing arm, a stylus carried by said arm, means for supporting said arm with a vertical axis of rotation remote from said stylus, means for causing the groove of a record disk to travel under said stylus in a general direction toward said vertlcal'axis, and means for applying a force to said reproducing arm, said means applying said force in a direction urging the reproducing arm toward a 1 position wherein the direction of travel of the groove under the stylus is tangent to the plane including the stylus point and said vertical axis, said means'being inactive when said stylus lies within a predetermined neutral reproducing sector.

6. In a stylus actuated translating device for a phonograph reproducer, a disk record, a styluscarrying arm mounted to swing over said record. an elongated spring member having one end fixed and having spaced contacts on the other end to engage said arm for urging it toward a neutral sector of the reproducing area when said arm lies on eitherside 01' said area.

7. In a stylus actuated translating device for a phonograph reproducer, a disk record, a styluscarrying arm mounted to swing over said record, a spring member having one end fixed and having a backlash engagement with said arm to urge said arm toward a neutral sector of the reproducing area-whenever said arm lies on either side of said area and thereby improve the tracking of said stylus.

8. In a stylus actuated-translating device for a phonograph reproducer, a disk record, a styluscarrying'.arni mounted to swing over said record,

a spring member having one end fixed and having a backlash engagement with said arm to urge said arm in a direction which will counteract the lateral component of the force of stylus friction and thereby improve the tracking of said stylus whenever said backlash is takenup.

= LINCOLN THOMPSON. 

